[PATCH 08/11] nouveau/gsp: don't free ctrl messages on errors

[Dan Carpenter]

On Thu, Jan 04, 2024 at 10:41:50AM +1000, Dave Airlie wrote:
> On Thu, 4 Jan 2024 at 00:47, Dan Carpenter <dan.carpenter at linaro.org> wrote:
> >
> > Hi Dave,
> >
> > kernel test robot noticed the following build warnings:
> >
> > https://git-scm.com/docs/git-format-patch#_base_tree_information]
> >
> > url:    https://github.com/intel-lab-lkp/linux/commits/Dave-Airlie/nouveau-gsp-drop-some-acpi-related-debug/20231222-180432
> > base:   git://anongit.freedesktop.org/drm/drm-misc drm-misc-next
> > patch link:    https://lore.kernel.org/r/20231222043308.3090089-9-airlied%40gmail.com
> > patch subject: [PATCH 08/11] nouveau/gsp: don't free ctrl messages on errors
> > config: powerpc-randconfig-r071-20231226 (https://download.01.org/0day-ci/archive/20231227/202312271917.55xuDMdc-lkp@intel.com/config)
> > compiler: clang version 18.0.0git (https://github.com/llvm/llvm-project d3ef86708241a3bee902615c190dead1638c4e09)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp at intel.com>
> > | Reported-by: Dan Carpenter <dan.carpenter at linaro.org>
> > | Closes: https://lore.kernel.org/r/202312271917.55xuDMdc-lkp@intel.com/
> 
> This is a false positive, I think the code is operating like I'd
> expect, we maybe could restructure it to avoid this warning?
> 
> The idea is you send an rpc msg, if there's a reply you get a reply,
> if no reply you get NULL and if an error you get an error.
> 
> So in the case you get an error or NULL you just want to return 0 for
> the NULL as it's successful, and error otherwise.
> 
> Would using PTR_ERR_OR_ZERO make smatch happy? (even if it's not
> really what we want).

Hm...  You're using the API correctly.  Linus has complained about this
warning before but in new code over 90% of the warnings are correct.
It's a high quality warning.

I looked around for an explanation to see what the NULL meant but
couldn't find it documented in the code.  The NULL vs error pointer comes
from a function pointer and it's not always clear where the
documentation should be with a function pointer.  So perhaps I missed it.

Let's not use PTR_ERR_OR_ZERO.  Perhaps I should introduce a
PTR_ERR_OR_NULL() macro to silence this warning.  But most of the code
which does this correctly is in fs/ and they probably are like Linus and
would be surprised to learn that people get it wrong...

regards,
dan carpenter